Ambitious automotive internal combustion engine emissions, fuel economy and performance goals require precise control of the ratio of air to fuel available for consumption in engine cylinders. Precise air/fuel ratio control requires compensation for fueling lags associated with the fuel injection system, including fueling lags caused by fuel film build-up on engine cylinder intake system components, such as valve poppets and intake passage walls. For a given fuel injection event, a portion of the fuel injected into a cylinder intake runner (passage) leading to an engine cylinder impacts the walls and intake valve poppet, leading to an accumulation or mass transfer of fuel film to such intake system components. That fuel film gradually depletes and is drawn, along with later injected fuel, into the engine cylinder during subsequent cylinder intake events, for combustion therein. The mass of fuel transferred to the intake system components and the time rate of depletion of that fuel is conventionally modeled as a boiling process.
For a given engine application, a substantial number of calibration parameters are required to account for the fuel mass transfer under the boiling process model. The need for a large set of calibration parameters is mainly due to the non-physical, weak relationship between the independent variables (i.e. intake manifold pressure and coolant temperature) used to schedule the parameters and the actual conditions occurring in the engine intake system. Accordingly, a significant amount of time is required to model the fuel mass transfer process each time an engine or engine intake system is changed, adding significant lead time and cost to engine development. Additionally, due to the lack of a clear underlying theory of parameter behavior, calibration parameter results vary significantly between applications due to differences in the approaches and expectations of calibration personnel.
It would therefore be desirable to provide a simplified model of the mass transfer process for transient internal combustion engine cylinder fueling control that accurately models the mass build-up and depletion of fuel film on the intake system, to provide for accurate control with reduced calibration burden.